1. Field of the Invention
The invention concerns keyboards in general but, more particularly, keyboards with alterable configurations wherein the keys may have different symbols as requested by the user, i.e. their configuration can be altered as regards both the symbols themselves and the display of these symbols.
Typewriters have keyboards with alterable configurations inasmuch as each key has two symbols attached to it, for example lower-case letters and capital letters. But the display of the symbol for the letters is not changed from one symbol to another, since only the capital letter is shown on the key. When the two symbols are very different, a figure and another sign for example, these two symbols are put on the key itself.
Computers as such or computers integrated in machines are controlled from control desks in which the main element is a keyboard which is often associated with a printer and a display device such as a cathode tube screen. To simplify and facilitate dialogue between the computer and the user, keyboards have numerous keys corresponding to alphanumerical characters, and each additional key corresponds to a well-defined function. This leads to a substantial increase in the number of keys as and when the number of functions increases for it is difficult to go beyond two symbols, hence beyond two displays, per key. Furthermore, this increase in the number of keys results in keyboards of increasingly greater sizes which are sometimes incompatible with certain applications.
2. Description of the Prior Art
A number of approaches have been proposed to solve this problem of changing the symbols related to the keys and the corresponding display.
In one of these methods, a symbol displaying device such as a liquid crystal array is integrated into each key, the display being controlled by electrical links combined with the motion of the key. In a solution of this type, the electrical links are complicated and the clarity of the display is reduced by soiling and by the deterioration of the anti-reflection treatment due to contact with fingers. Furthermore, in general, the cost price of a keyboard of this type is high because of the cost of the mechanical device of the keys for electrical links.
In a second approach, a transparent film with integrated contacts is deposited on a display screen which displays the symbols related to the contacts. A device of this type has the chief disadvantage of giving a view affected by the parallax, unwanted reflections, losses in transmission and soiling due to contact with fingers. Moreover, there is no mechanical sensation of contact with the key, which the operator needs even if each action of the key is accompanied by a sound signal.
In a third approach, a set of light-emitting diodes is arranged on the periphery of a display screen. These light-emitting diodes are associated with photo-detectors or photo-sensitive cells so as to create a matrix arrangement of lines and columns, each line and column being defined by a light-emitting diode and a light-sensitive cell. Each key corresponds to an intersection of a line and a column, and its associated symbol is displayed on the display screen at each intersection. Thus a key is chosen by an operator's finger which intercepts the light ray from a line and a column thus defining the position of the key and, hence, the symbol attached to it. A device of this type has the following disadvantages: there is no mechanical sensation in the choice of a "key"; there is a risk of jamming following the interposing of a mask in the light beams of the lines and columns; a line or column of keys may be lost if the transmitter or corresponding receiver malfunctions and there are unwanted reflections on the surface of the display screen if the light beams are not sufficiently directional and narrow.
An aim of the present invention is to make a keyboard with a special type of alterable configuration which does not have the above-mentioned disadvantages of prior art keyboards and uses at least one flat display panel and at least one row of keys as well as associated electronic circuits.
Another aim of the present invention is a keyboard with an alterable configuration organized into two independent parts, each part being capable of functioning in back-up mode in the event of a malfunction in the other part.
Yet another aim of the present invention is a keyboard with a alterable configuration which enables the immediate display of messages, especially the symbol associated with the key actuated by the user.